1. Field of the Invention
The present invention relates to an elastic coupling, and more particularly to an improved elastic coupling to which a novel theory is applied.
2. Description of the Prior Art
A power transmission mechanism for a prime mover or driven mechanism having a reciprocating mechanism is well known to have concomitant drawbacks such as variations in torque or torsional vibrations or impacts, all of which are detrimental to the mechanical parts or shaft systems of the power transmission mechanism. In this power transmission mechanism, therefore, an elastic coupling is frequently used for absorbing and damping or blocking those detrimental phenomena so as to continue safe drive of the transmission mechanism. Especially in recent years, more severe conditions are being imposed upon the elastic coupling as the requirements for high output and speed of the prime mover and for improvement in economy of the transmission mechanism become stronger. The elastic coupling now in practical use has a number of types and kinds, which have respective advantages and disadvantages. It can be concluded here that the excellency of an elastic coupling is enhanced by meeting requirements such as the requirement for correct transmission of drive power, the requirement for the driven portions to be protected from the applied vibrations or noises or to enjoy prolinged life time, or the requirement for the performance of the elastic coupling to be raised or equalized.
The most important condition, with which an elastic coupling should be furnished, is sufficient elasticity. For this purpose, a metal spring of leaf or coil type, a rubber tube filled with air or a viscous medium, a rubber or elastomer element, and the like are used as an elastic element for the elastic coupling. Thus, the elastic coupling made of rubber or the like is most frequently used for its excellent effects, such as, its wide applicability to a load of multi-directionality in compression, shear and torsion, and the effective damping, noise-blocking and insulating performances, excepting for its durability.
In order to enhance durability of the elastic coupling using an elastic element of rubber or an elastomer, a variety of devices have been made and put into actual practice, including one of the most effective coupling, which is shown in FIGS. 1 and 2 of the accompanying drawings. The elastic coupling of FIG. 1 is composed of three metal rings 1, 2 and 3, and of rubber rings 4 and 5 which are interposed between the metal rings 1, 2 and 3 and which are fitably secured thereto by a vulcanizing treatment. Each of these rubber elements 4 and 5 is divided into halves with respect to the longitudinal direction of the elastic coupling. If, however, the number of the rubber elements is other than two, it will be easily understood that each of them is also divided into halves in the longitudinal direction. As is apparent from FIG. 1 showing the elastic element under the free condition before it is assembled with its halves confronting each other, a longitudinal spacing S is formed between the divided halves of the outer metal ring 1. In FIG. 2, on the other hand, the elastic coupling is shown as under the assembled condition, in which the halves of the outer metal ring 1 are fixed to each other by means of bolts 9 (although not concretely shown) with the spacing S reduced to zero. Reference will now be made to FIG. 3, in which the illustration of the elastic coupling is enlarged to explain its fixed condition. In FIG. 3, the solid lines show the elastic coupling under the free condition before it is assembled, while the broken lines show the elastic coupling under the assembled condition. Those sufaces of the metal rings 1, 2 and 3 and of the rubber elements 4 and 5, which are to be secured to each other by the vulcanizing treatment, are inclined to have a conical cross-section, as shown by the solid lines. As a result, when the halves of the outer metal ring 1 are pushed into contact with each other, the rubber rings will be subjected, as shown by the broken lines, to deformation, which takes place in the direction perpendicular to that of torque transmission of the rubber rings. In FIG. 3, more specifically, the radial height l of the whole rubber element under the free condition will be reduced to l' due to the deformation after the elastic coupling is assembled. The difference, .DELTA.l, in the heights before and after assembly will impart a pushing forth to the inclined contact surface of the metal rings 1, 2 and 3 and of the rubber rings and at the same time will impart a compression to the insides of the rubber rings. This compression is called as the "precompression", because it is preliminarily imparted to the rubber rings during the assembly process before a torque is transmitted to the elastic coupling. It is widely admitted that application of the precompression will result in effectiveness in strengthening adhesiveness by the vulcanizing treatment and in heightening the anti-wear strength of the rubber element. As an example of the material based on the above theory, pre-stressed concrete is well known, which aims at similar effects. One of the disadvantages, which are concomitant with the coupling rubber element of the pre-compression construction, is that the resultant effects coming from the pre-compression treatment cannot be expected uniformly in all portions of the rubber element from the deformation due to the compression. In the rubber element of the compression type, more specifically, since its design is made assuming that the radial shearing stress is identical for any portion, the cross-section of the rubber element taken in the radial direction is formed such that the thickness of the element (taken in the direction perpendicular to the radial direction, namely, in the longitudinal direction) assumes such a value as is inversely proportional to the radius. As will be easily understood, a compressive stress is established on the surface of the rubber element which is pulled during the pre-compression treatment, whereas a tensile stress is built up on substantial surface of the opposite side. This tendency is found not only on the surfaces of the rubber element but also internally and on such surfaces of the element as are to be secured to the metal rings by the vulcanizing treatment. In a mechanical element such as an elastic coupling, reduction in local durability due to the irregular quality coming from its particular construction will hardly fail to lead to material reduction in durability of the elastic coupling as a whole. This undesirable phenomenon is confirmed by the experiment, in which the pre-compression treatment adversely affects partially the elastic coupling.
On the other hand, when it is intended to shift one half of the outer metal ring 1 or FIG. 1 by the distance half of the spacing S with respect to one half of the adjoining rubber ring 4, such a great force is required as can compress the total height of the rubber rings 4 and 5 by the length .DELTA.l. In order to obtain the inter balance in the forces including that great force, moreover, the confronting halves of the rubber rings are required to be fastened to each other, as shown in FIG. 2. This means that the division of the rubber element into two halves is an indispensable condition for an elastic coupling. This condition in turn becomes unfavourable for the elastic coupling to be assembled or disassembled.